Contents

Bismuth-209 was long thought to have the heaviest stable nucleus of any element, but in 2003, a research team at the Institut d’Astrophysique Spatiale in Orsay, France, discovered that 209Bi undergoes alpha decay with a half-life of approximately 19 exayears (1.9×1019 which is 19 quintillion years), over a billion times longer than the current estimated age of the universe. Theory had previously predicted a half-life of 4.6×1019 years. The decay event produces a 3.14 MeV alpha particle and converts the atom to thallium-205.[1][2]

Due to its extraordinarily long half-life, for nearly all applications 209Bi can still be treated as if it were non-radioactive. Although 209Bi holds the half-life record for alpha decay, bismuth does not have the longest half-life of any radionuclide to be found experimentally—this distinction belongs to tellurium-128 (128Te) with a half-life estimated at 7.7 × 1024 years by double β-decay (beta decay).[4]

The half-life value of Bismuth-209 was confirmed in 2012 by an italian team in Gran Sasso who reported 2.01±0.08 ×1 019 years, and an even longer half-life, for bismuth-209 alpha decay to the first excited state of Thalium-205 at 204keV, which was estimated to be 1.66×1021 years[5]. Even if this value is shorter than the measured half-life of tellurium-128, both alpha decays of Bismuth-209 hold the record of the thinnest natural line widths of any measurable physical excitation, estimated respectively at ΔΕ~5.5×10-43 eV and ΔΕ~1.3×10-44eV in application of the uncertainty principle of Heisenberg[6] (double beta decay would produce energy lines only in neutrinoless transitions, which has not been observed yet).

In the red giant stars of the asymptotic giant branch, the s-process (slow process) is ongoing to produce bismuth-209 and polonium-210 by neutron capture as the heaviest elements to be formed, and the latter quickly decays. All elements heavier than it are formed in the r-process, or rapid process, which occurs during the first fifteen minutes of supernovas.[8]